Modulating carrier waves



Apri12o,192e. y 1,531,295

` J. W. SCHMIED MODULATING GARRI ER WAVES Filed August 26, 1922 w law Patented Apr. 20, 192.6

A,Umruu S'rATas parametrica.

. -JAMEs W. SCHMIED, OE WEST ORANGE, NEW JEEsEY, AssreNoE To WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF yNEW YORK, N. Y., .A CORPORATION OE NEW `YORK.

MODLATING CAEEIEEWAvEs.`

Application led August 2 6, 1922. Serial' No, 584,412.

To all whom 'it may concern:

Beit known that I, JAMES W. SoHM1ED,a citizen of the United States of America, residing at WestOrange. in the county of Es- 5 sex and State of New Jersey, have invented certain,L new and useful Improvements in Modulating Carrier Waves. ofv which the following is a full, clear, concise, and exact description. l l .c l

' This invention'rel'ates to systems for, and

methods of, modulating Acarrier waves 1n accordance with signals and more particularly to constant current and constant volttelephony. v One object of the invention is to simpllfy systems of the type' which produce and transmit modulated waves from which the unmodulated component hasbeen wholly or partly suppressed. f K

e Another object is to increase the' high frequency voltage which is impressed upon the transmittingcircuit without utilizing a cori respondingly increased voltage of the space currentsupply source of a vacuum tube sys? tem which produces the waves to be transmitted. t Y

The invention is herein illustrated in systems in'which two vacuum tube oscillators are connected to a tuned frequency determining antenna. The oscillators are so related tothe antenna that the high frequency voltages produced by the oscillators will Abe impressed in series upon the antenna circuit. Each oscillator has an output circuit coupled iage modulation systems for yuse in radio 'l c Vof ay const-antvoltage modulating system em associated with it an output or plate circuit to the antenna and a feed-back couplingl connected to the antenna in opposing rela-g tubes of the generators maykh'ave their cath odes connected to a common point and grounded. In the constant voltage type of rcircuit, the cathodes of the oscillator tubes -and of the variable impedance tubes cannotv .both be grounded by connections'conductive vto direct or speech frequency currents. It

i s preferred to ground the oscillator cathodes as shown. y f

Constant current`and constant voltage 50 systems are known. See the articleA by R. A.' Heising in the Proceedings of the I. R. E.

August, 1921. 1 Y

In the drawing, Fig. 1 is a-circu'it diagram 65 bodying the invention andFig. 2 is a circuit 'diagram of a constant currentv or shunt modulating system.

In Fig. 1, each vacuum tube 1 and 2 has 70 extending from the anode through a con` f denser 3, a coil 1, and the common condenser 5. The plate circuits are coupled to the antenna circuit 6 by means of the coupling between the coils 11 and the fixed and movable coils 7 and 8, respectively." The fixed coils 9, and the movable coils 8, are also coupled to coils 10 in the grid or input circuits of the vacuum tubes. Stopping condensers 11 in each input circuit and the usual high resist- ,80 an'ces 12 are provided. The source 13 sup- I plies space or anode-cathode current to the tubes 1 and 2. Switchesl are provided so that space current may, if desired, be supplied throughl a speech frequency choke coil $5 15. The purpose of the coil 15 is to'make the suppression of the unmodulated carrier component more complete. vIn series with the tube 1` is the anode-cathode path of the tube 21 andy in series with the' tube 2 is the anode-cathode path ofthe tube 22; High frequency choke coils 23, ofllow'impedance to speech frequencies, prevent the high frequency waves, generated by the. oscillators, from being dissipated in the tubes 21 and 22 and their associated circuits. Incoming waves from a microphone circuit or telephone line 2li are impressedup'on the input or grid-filament circuits of tubes 21 and 22. 160 In each grid circuit is included a portion ofy amplitude, the tube 2 will be generating' waves of lower than average amplitude. When no signaling waves are being applied to the input circuits of the modulating tubes the amplitude of the high frequency waves in the antenna will be small or zero because the oscillators are connected to the antenna in opposing relation. rlhe input and output circuits of the two oscillator tubes are equal'- ly coupled to the antenna circuit. rlhe two systems of coils 7, 8, 9 are alike and the coils 8 are to be adjusted to approximately the same position for a given wave length.

In Fig. 2, the antenna circuit is indicated as having two high frequency coils 26 in series. The plate and grid circuit coils 4 and 10 of each oscillator are coupled to one of the coils 26. The coils 4 and lO are preferably variable both as to number of turns and as to their position with respect to coils 26. Coil 26 vmay also have a variable number of turns if desired. The coupling coil arrangements of Figs. l and 2 are interchangeable. The remaining elements of the high frequency oscillators bear reference numerals corresponding to the elements of Fig. 1 and function in a similar manner.

The modulating system in Fig. 2 is of the constant current type, that is, a source 13 supplies current through a speech frequency choke coil 27 to the oscillating tube l and the cooperating modulating tube 21 in parallel. Coil 27 has such high inductive reactance at speech frequencies that practically constant current is supplied through it. A similar coil 27 is connected in circuit with the oscillating tube 2 and its cooperating modulating tube 22. The tubes 2 and 22 consequently constitu-te a second constant current modulating system connected to the antenna circuit in opposed relation to that constituted by tubes l and 21. The elements 24 and 25 function to vary the impedances of the tubes 2 and 2l as is described in connection with Fig. l.

approximately 180o out-of-phase with each other.

Although described in connection with radio systems the principles of the invention are applicable in systems foi signaling 1. A radio transmitting circuit consisting v of two electrically symmetrical circuits, each comprising a modulator tube and an oscillator tube, a common signal frequency input source for said circuits, means for preventing the oscillationgenerator tube from being short circuited by the modulator-tube of each circuit, and means for coupling the oscillator tubes tov an antenna circuit. V 2. A radio transmission system comprising two electrically symmetrical circuits,

each comprising a modulator tube and a high frequency tube, a speech frequency circuit oppositely coupled to said modulator tubes to vary the impedance thereof, and means for coupling the high frequency tubes oppositely to an antenna circuit.

3. A modulating system comprising a plurality of constant current modulating systems each comprising a high frequency discharge device and a variable impedance disf charge device, said variable impedance devices having a common low frequency input circuit and said high frequency devices being coupled to a common high frequency output circuit.

4. A modulating system comprising two electrically symmetrical constant current modulating systems, each comprising a variable impedance device and a carrier Wave generating device in parallel with respect to a common source of current/and a speech frequency choke coil; a common speech frequency input circuit oppositely connected to said variable impedance devices, and a common high frequency output circuit for the said carrier wave generating devices.

5. A modulating system comprising a source of current, means for maintaining a constant iiow of current from said source, parallely paths having a common portion through said source, each of said paths including a high frequency discharge device and a low frequency discharge device, means for varying the impedance of said high frequency discharge device at a carrier frequency rate, and means foi' varying the impedance of said 10W frequency discharge device at a modulating frequency rate.

6. An inductance coil having high impedance at speech frequencies, a source of cur- 5 rent in series therewith, two paths in paraHel with respect to said source and coil,

each of said paths containing two discharge devices, and means for varying the impedance of one devicev in each path at a high frequency and the other at a low frequency.l

In witness whereof, I hereunto subscribe my name this 23rd day of August A. D., 

